Sorry you're going through this. At my last company we were in a similar spot to you - around ~$700/mo spending for Twilio. We had issues where they also were shutting us off and were unresponsive for days at a time. Once we had a rollout with a few dozen new clients in an area where we hadn't sent texts before and after sending a few thousand messages we were shut off at the carrier level. We tried reaching out for a day or two and really didn't get much back in response - to us this was the final straw and we moved to bandwidth.com (which I believe is who google uses for their auth).

Support with them is significantly better but if I remember correctly pricing is around $1k/mo minimum (which was more than worth it in our case).

Best of luck to you.